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 (b) For a rectangular tied column with equal reinforcement on
opposite faces (Figure 36a), the ultimate axial load capacity at a given
eccentricity is approximated by:
As fdy
bh f'dc
EQUATION:
Pu = +
(62)
e/(2d-h) + 0.5
3he/d2 + 1.18
where,
Pu = ultimate axial load at e, lb
e = actual eccentricity of applied load
As = area of reinforcement on one face of the
section, in2
d = distance from extreme compression fiber to
centroid of tension reinforcement, in
h = depth of rectangular section, in
b = width of rectangular section, in
For a circular section with spiral reinforcement, the ultimate axial load
capacity at a given eccentricity is approximated by:
(6) Tension Controls.
(a) When the ultimate eccentric load, Pu, is less than the
balance value, Pb, or when the eccentricity, e, is greater than the
balanced value, eb, the member acts more as a beam than as a column.
Failure of the section is initiated by yielding of the tension steel. The
ultimate eccentric load at a given eccentricity, e, greater than eb may be
obtained by considering the actual strain variation as the unknown and using
the principles of statics. However, Whitney's equations may again be used
to approximate the capacity of the column. It should be pointed out that
while tension controls a possible design situation it is not a usual
condition for interior columns of a shear wall type structure.
2.08-95
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